Sodium bicarbonate, commonly known as baking soda, is traditionally used as a leavening agent in the food industry. It is also widely used in household, personal care and industrial applications. There are two typical industrial processes for manufacturing sodium bicarbonate; the Solvay process and Trona ore mining.
Sodium bicarbonate is an intermediate product of the Solvay process, whose targeted end product is sodium carbonate. In the Solvay process, ammonia and carbon dioxide are sparged through a saturated sodium chloride solution to form a solution containing ammonium bicarbonate. This ammonium bicarbonate is then reacted with sodium chloride to form ammonium chloride and sodium bicarbonate. Ammonium chloride is very soluble, and the much less soluble sodium bicarbonate is precipitated and crystallized, if the temperature is kept below 15° C. The precipitated sodium bicarbonate is filtered off, heat is applied to decompose it and sodium carbonate is obtained as the desired end product.
A second manufacturing process is based on Trona ore, a sodium sesquicarbonate mineral ore (Na2CO3.NaHCO3.2H2O), mined mostly in Wyoming, USA. The ore is first crushed and screened. It is then calcined to raw sodium carbonate, carbon dioxide and water. The sodium carbonate is dissolved and filtered to eliminate impurities. Carbon dioxide is bubbled into the saturated pure sodium carbonate solution and the sodium bicarbonate precipitates out to be collected and dried. Trona ore mining is the most dominant process for producing sodium bicarbonate in North America because it is cheaper to mine the ore than to synthesize NaHCO3 from other raw materials.
Foaming plastics and rubbers is a known industrial application of sodium bicarbonate. After NaHCO3 is added into melted plastics or rubber material, it decomposes releasing carbon dioxide. The formation of gas bubbles results in a cellular foam structure.
Among the numerous desirable attributes achieved by the foaming of plastics and rubber materials are energy absorption, low thermal conductivity, sound absorption, low thermal conductivity for insulation properties, cushioning, soft and flat surfaces, high strength/weight ratios for good strength and softness, improved thermal strength and thermal and chemical inertness.
A number of patents are directed to the preparation of sodium bicarbonate powder having small particle size or other particular useful physical characteristics such as substantial sphericity of the sodium bicarbonate particles [published U.S. Patent Application No. 2002/0172713-Einzinger et al and microporosity, U.S. Pat. No. 5,482,701 (Winston)].
Very fine or ultrafine sodium bicarbonate powders have been prepared by a number of methods. U.S. Pat. No. 5,411,750 (Lajoie et al.) describes the precipitation of sodium bicarbonate from aqueous solution by the gradual addition of a water-miscible organic solvent such as CH3OH. This is claimed to produce sodium bicarbonate powder having an average particle size less than about 1 micron, but with a broad particle size distribution, between about 0.1 and 1 micron.
U.S. Pat. No. 6,352,653 (Hirano et al.) is said to produce sodium bicarbonate having a volume-based mean particle diameter of from 1 to 9 microns. This sodium bicarbonate powder is obtained by grinding NaHCO3 using an impact-type grinder equipped with an air classifier, which classifies particles discharged from the grinder and returning large particles to the grinder.